Optical agents play a central role in a large number of in vivo, in vitro and ex vivo clinical procedures including important diagnostic and therapeutic procedures. Photodiagnostic and phototherapy agents, for example, include a class of molecules capable of absorbing, emitting, or scattering electromagnetic radiation applied to a biological material, particularly in the visible and near infrared regions of the electromagnetic spectrum. This property of optical agents is used in a range of biomedical applications for visualizing, imaging or otherwise characterizing biological materials and/or achieving a desired therapeutic outcome. Recent developments in targeted administration and delivery of optical agents, and advanced systems and methods for applying and detecting electromagnetic radiation in biological environments, has considerably expanded the applicability and effectiveness of optical agents for many clinical applications.
Important applications of optical agents that absorb and/or emit in the visible and near-infrared (NIR) region of the electromagnetic spectrum include their use in biomedical imaging and visualization. Imaging and visualization using such optical agents has potential to provide a less invasive and safer imaging technology, as compared to X-ray, and other widely used nuclear medicine technologies. Applications of optical imaging for diagnosis and monitoring of the onset, progression and treatment of various disease conditions, including cancer, are well established. (See, e.g., D. A. Benaron and D. K. Stevenson, Optical time-of-flight and absorbance imaging of biologic media, Science, 1993, 259, pp. 1463-1466; R. F. Potter (Series Editor), Medical optical tomography: functional imaging and monitoring, SPIE Optical Engineering Press, Bellingham, 1993; G. J. Tearney et al., In vivo endoscopic optical biopsy with optical coherence tomography, Science, 1997, 276, pp. 2037-2039; B. J. Tromberg et al., Non-invasive measurements of breast tissue optical properties using frequency-domain photon migration, Phil. Trans. Royal Society London B, 1997, 352, pp. 661-668; S. Fantini et al., Assessment of the size, position, and optical properties of breast tumors in vivo by noninvasive optical methods, Appl. Opt., 1998, 37, pp. 1982-1989; A. Pelegrin et al., Photoimmunodiagnosis with antibody-fluorescein conjugates: in vitro and in vivo preclinical studies, J. Cell Pharmacol., 1992, 3, pp. 141-145).
In addition to their important role in biomedical imaging and visualization, optical agents capable of absorption in the visible and NIR regions have also been extensively developed for clinical applications for phototherapy. The benefits of phototherapy using optical agents are widely acknowledged as this technique has the potential to provide efficacy comparable to radiotherapy, while entirely avoiding exposure of non-target organs and tissue to harmful ionizing radiation. Photodynamic therapy (PDT), in particular, has been used effectively for localized superficial or endoluminal malignant and premalignant conditions. The clinical efficacy of PDT has also been demonstrated for the treatment of various other diseases, injuries, and disorders, including cardiovascular disorders such as atherosclerosis and vascular restenosis, inflammatory diseases, ophthalmic diseases such as age related macular degeneration and dermatological diseases. Visudyne® and Photofrin®, for example, are two optical agents that have been developed and approved by the FDA for the treatment of macular degeneration of the eye and for ablation of several types of tumors, respectively. (See, e.g., Schmidt-Drfurth, U.; Bringruber, R.; Hasan, T. Phototherapy in ocular vascular disease. IEEE Journal of Selected Topics in Quantum Electronics 1996, 2, 988-996; Mlkvy, P.; Messmann, H.; Regula, J.; Conio, M.; Pauer, M.; Millson, C. E.; MacRobert, A. J.; Brown, S. G. Phototherapy for gastrointestinal tumors using three photosensitizers—ALA induced PPIX, Photofrin, and MTHPC. A pilot study. Neoplasma 1998, 45, 157-161; Grosjean, P.; Wagieres, G.; Fontolliet, C.; Van Den Bergh, H.; Monnier, P. Clinical phototherapy for superficial cancer in the esophagus and the bronchi: 514 nm compared with 630 nm light irradiation after sensitization with Photofrin II. British Journal of Cancer 1998, 77, 1989-1955; Mitton, D.; Ackroyd, R. Phototherapy of Barrett's oesophagus and oesophageal carcinoma—how I do it. Photodiagnostics and Phototherapy 2006, 3, 96-98; and Li, L.; Luo, R.; Liao, W.; Zhang, M.; Luo, Y.; Miao, J. Clinical study of photofrin phototherapy for the treatment of relapse nasopharyngeal carcinoma. Photodiagnostics and Phototherapy 2006, 3, 266-271).
Phototherapy is carried out by administration, and preferably targeted delivery, of a photosensitizer to a target tissue (e.g., tumor, lesion, organ etc.) followed by photoactivation of the photosensitizer by absorption of applied electromagnetic radiation, typically provided by a laser light source. Phototherapy targets include tumor cells, tumor microvaculature, inflammatory cells, immune host cells and neovascular endothelium cells. The applied electromagnetic radiation excites the photosensitizer, resulting in formation of reactive species capable of initiating a cascade of cellular and molecular events eventually resulting in selective target tissue destruction.
Photosensitizers may operate via two different major pathways, classified as Types 1 and 2. The Type 1 mechanism proceeds via a two-step process involving activation of the photosensitizer by applied electromagnetic radiation followed either by direct transfer of the energy from the excited state of the photosensitizer to the tissue, or though the interaction of reactive intermediates (e.g., radicals, ions, nitrene, carbene etc.) derived from the excited photosensitizer with the target tissue, resulting in tissue damage. The Type 1 mechanism can be represented by the following sequence of reactions:Step 1: PHOTOSENSITIZER+hv(PHOTOSENSITIZER)*  (1)Step 2: (PHOTOSENSITIZER)*+TISSUE→TISSUE DAMAGE  (2)wherein hv indicates applied electromagnetic radiation and (PHOTOSENSITIZER)* indicates photoactivated photosensitizer. The Type 2 mechanism proceeds via a three-step process involving activation of the photosensitizer by absorption of electromagnetic radiation followed by energy transfer from the activated photosensitizer to oxygen molecules in the environment of the target tissue. This energy transfer process generates excited state oxygen (1O2) which subsequently interacts either directly or indirectly through Reactive Oxygen Species (ROS) with the target tissue so as to cause tissue damage. The Type 2 mechanism can be represented by the following sequence of reactions:Step 1: PHOTOSENSITIZER+hv(PHOTOSENSITIZER)*  (3)Step 2: (PHOTOSENSITIZER)*+3O2 (Triplet Oxygen)→1O2 (Singlet Oxygen)  (4)Step 3: 1O2 (Singlet Oxygen)+TISSUE→TISSUE DAMAGE  (5)wherein hv indicates applied electromagnetic radiation, (PHOTOSENSITIZER)* indicates photoactivated photosensitizer, 3O2 is ground state triplet oxygen, and 1O2 is excited state singlet oxygen. As shown by reactions 1 and 2, Type I photosensitizers do not require the presence of oxygen for causing tissue damage, and therefore, are expected to be more effective than Type II photosensitizers under extremely hypoxic environments often found in solid tumors.
The biological basis of tissue injury brought about by tumor phototherapy agents has been the subject of intensive study. Various biochemical mechanisms for tissue damage have been postulated, which include the following: a) cancer cells up-regulate the expression of low density lipoprotein (LDL) receptors, and phototherapy (PDT) agents bind to LDL and albumin selectively; (b) porphyrin-like substances are selectively taken up by proliferative neovasculature; (c) tumors often contain increased number of lipid bodies and are thus able to bind to hydrophobic photosensitizers; (d) a combination of “leaky” tumor vasculature and reduced lymphatic drainage causes porphyrin accumulation; (e) tumor cells may have increased capabilities for phagocytosis or pinocytosis of porphyrin aggregates; (f) tumor associated macrophages may be largely responsible for the concentration of photosensitizers in tumors; and (g) cancer cells may undergo apoptosis induced by photosensitizers. Among these mechanisms, (f) and (g) are the most general and, of these two alternatives, there is a general consensus that (f) is the most likely mechanism by which the phototherapeutic effect of porphyrin-like compounds is induced.
Not withstanding the numerous benefits of phototherapy, these techniques are not without some drawbacks. For example, local hypoxia is an inherent consequence of phototherapy under some conditions. Local hypoxia may arise directly from oxygen consumption during treatment and/or indirectly from disruption of tumor vasculature as a result of treatment. Tissue hypoxia induces a range of molecular and physiological responses including an angiogenesis response associated with gene activation. For example, hypoxia mediated gene activation is believed to proceed via stabilization of the transcription factor hypoxia-inducible factor-1α (HIF-1α), which binds to the HIF-1α response element (HRE) in the promoter of a number of genes including the vascular endothelial growth factor (VEGF) gene. Vascular endothelial growth factor is an angiogenic molecule involved with the induction and maintenance of neovasclature in solid tumors. Animal studies have documented an increase in VEGF production and accelerated angiogenesis response after phototherapeutic treatment. (Momma, T; Hamblin, M. R.; Wu, H. C.; Hasan, T; “Photodynamic Therapy of Orthotropic Prostate Cancer with Benzoporphyrin Derivative: Local Control and Distant Metastasis”, Cancer Research, 58, 5425-5431, December 1998.) As a result of increased secretion and stabilization of vascular endothelial growth factor (VEGF) in response to some phototherapy procedures, unwanted tumorigenesis and metastasis processes can be initiated. Accordingly, a number of combination therapy strategies for inhibiting this endogenous angiogenic response are being pursued as means to enhance the therapeutic efficacy of phototherapy.
A number of anti-VEGF compounds have been evaluated in the context of a combination therapy for the treatment of age related macular degeneration. U.S. Patent Publication US 2003/0171320, by D. R. Gruyer and published Sep. 11, 2003, discloses methods for treating ocular neovascular disease using anti-VEGF compounds, including aptamers and antibodies, alone or in combination with photodynamic therapy or thermal laser photocoagulation. This reference discloses a number of anti-VEGF aptamers such as nucleic acid ligands having 2′-F-modified nucleotides, 2′-O-methyl nucleotides, and pegylated aptamers and generally refers to therapeutic procedures using VEGF antibodies and fragments thereof. The clinical results provided suggest that combining administration of an anti-VEGF agent with phototherapy enhances efficacy for treatment of age related macular degeneration in certain patients. U.S. Patent Publication US 2003/0026945, by Gomer et al. and published Mar. 7, 2002, discloses methods for photodynamic therapy including administration of an anti-VEGF agent to improve tumoricidal activity. This reference discloses a single chain polypeptide, EMAP-II, having anti-angiogenic activity reportedly capable of inhibiting tumor growth and a dipeptide of L-glutamyl-L-tryptophan, IM862, that reportedly inhibits angiogenesis and VEGF production in monocytic lineage cells. PCT International Publication No. WO 2009/117669, published on Sep. 24, 2009, describes treatment with opioid antagonists and mTOR inhibitors in the context of cellular proliferation and migration.
Several antibody conjugates have recently been developed including pegaptanib (Macugen®), bevacizumab and ranibizumab for antagonizing VEGF mediated angiogenesis. Bevacizumab is a full-length humanized monoclonal antibody against vascular endothelial growth factor and has been commercialized as Avastin®. Ranibizumab is a humanized anti-VEGF antibody fragment derived from bevacizumab which inhibits VEGF activity by competitive binding and has been commercialized as Lucentis®. In the context of macular degeneration treatment, Avastin® and Lucentis® have been shown to stop abnormal vessels from growing and leaking but often don't cause permanent closure, and therefore, injections of either drug have to be given repeatedly. Phototherapy on the other hand has been demonstrated as effective for permanently closing vessels but can result in vision loss under some conditions. A combination therapy has recently been developed involving phototherapy with half the amount of laser dose followed with an injection of Lucentis® or of Avastin® and optionally with administration an anti-inflammatory steroid. (Augustin, A J, Puls, S, Offerman I, “Triple Therapy for Choroidal Neovascularization due to Age-Related Macular Degeneration. Vertportfrin PDT, Bevacizumab, and Dexamethasone. RETINA 27:133-140, 2007.).
One problem with Type 2 phototherapy procedure is the induction of inflammatory response due to reactive oxygen species produced by photoexcitation of oxygen by Type 2 photosensitizers. This inflammatory response causes the blood vessels to become more porous and, hence, allows cancer cells to metastasize to other regions. As will be generally recognized from the foregoing, a need currently exists for enhancing the therapeutic efficacy of phototherapy by preventing metastasis, and for the treatment of macular degeneration using agents that are capable of inhibiting inflammatory response, including, but not limited to the expression and/or activity of vascular endothelial growth factor.